1. Field of the Invention
The present invention relates to ink jet recording and more particularly, to improved methods for fabricating an ink jet droplet generator.
2. Prior Art
Ink jet recording is a rather sophisticated technique for recording information on a recording medium such as paper or the like. In a conventional impact printer, a well-defined or shaped stylus or type element impacts the record medium to leave an ink impression of the type element. In ink jet printing, however, a sequence of individual ink droplets strike the record member in a controlled pattern to duplicate impressions previously formed by the conventional impact technique.
A variety of ink jet printing architectures have evolved. A common element to these architectures is a mechanism for directing ink droplets toward the record medium. Architectures, for example, have been proposed which utilize single ink nozzles which pass the record medium at high speed while continually emitting a stream of ink which breaks up into ink droplets. Single nozzle arrangements have been contemplated for so-called "drop-on-demand" systems wherein ink droplets are only generated when the nozzle approaches a specific portion of the recording member and so-called continuous systems wherein the single nozzle continuously generates ink droplets which are either directed to a specific recording medium pixel or guttered to a recirculating system for reuse.
Rather than using a single ink droplet nozzle to rapidly traverse across a record medium, proposals have been made for developing an array or plurality of ink droplet nozzles spaced across a record medium for generating a number of streams of ink recording droplets. In particular, one architecture envisions stationary nozzles each of which directs a droplet stream toward the record medium along an initial path parallel to the plurality of other ink jet trajectories. Subsequent to droplet production, these proposals include droplet charging and deflecting mechanisms downstream from the droplet generator for interacting with the droplets, changing their trajectory and thereby directing the droplets to desired positions on the recording member. As seen in the literature, it is very important that the ink droplets which are provided by the ink jet recording system are properly charged as they travel toward the record medium so that they can be properly deflected. To facilitate droplet charging it is important that droplet production occur at well-defined locations with respect to the drop generator. A typical ink jet system includes a mechanism for exciting or perturbing the ink as it is squirted from the nozzle, thereby inducing droplet production in appropriate relation to a charging electrode.
In multi-jet ink jet systems, alignment of multiple ink nozzles has presented problems in array fabrication. Small variations in nozzle dimensions and alignment can be tolerated but these tolerances are quite small. One multi-nozzle array envisions the multiple nozzles having a diameter of 0.001 in. and an alignment accuracy of 2 mrad. The achievement of these rather stringent tolerances in ink jet drop generator fabrication has been a non-trival task.
One suggested fabrication method involves selective etching of nozzle openings through a thin nozzle plate which is then mounted to an ink jet generator. Co-pending U.S. application Ser. No. 245,422 filed Mar. 19, 1981 to Pollack, for example, discloses a procedure for fabricating a nozzle plate from nickel and copper using a photoresist to define nozzle openings in the nickel as the nickel is plated onto the copper.
The Pollack and other similar plate fabrication methods suffer a common deficiency. Once the nozzle plate has been fabricated the plate must be mounted to an ink cavity into which ink under pressure is forced so that the nozzles in the multi-nozzle array squirt ink droplets toward the record member. In affixing the nozzle plate to the cavity, nozzles can be misaligned due to bending of the nozzle plate and/or due to irregularities in the surface to which the plate is affixed. Thus, although the etching technique for developing the nozzles may produce nozzle structures well within the desired tolerances, the step of physically attaching this nozzle plate to the remaining portions of the ink jet droplet generator can introduce ink stream inaccuracies beyond the tolerable limits suggested above.